Situating a thick polysilicon functional layer over a thin buried polysilicon layer is generally known for manufacturing MEMS structures. The buried polysilicon layer is used in this case as a printed conductor or an electrode. The polysilicon functional layer is typically exposed via a trenching process and a sacrificial layer etching method.
A micromechanical system and a corresponding manufacturing method are known from DE 10 2007 060 878 A1, a second buried polysilicon layer being provided, which may be exposed like the first polysilicon functional layer. This layer may be used as a printed conductor, so that, for example, printed conductor intersections are also possible as a printed conductor in combination with the first buried polysilicon layer. The second buried polysilicon layer may also be used as a mechanical freestanding layer. The three layers are separated by oxide layers, which are also used as sacrificial layers. The oxide layers define the distance between the individual layers and are designed to be relatively thick, depending on the application. If connections are applied between the layers, a tall topology is created on the surface, which makes it more difficult to manufacture structures at high resolution. The smaller the contact surfaces are designed, the less the influences by the elevated topography; however, the mechanical stability of the connection is thus simultaneously greatly reduced.
On the one hand, the oxide layers between the individual polysilicon layers may be intentionally used for mechanical reinforcement. On the other hand, mechanical tensions may occur due to the different mechanical parameters, however, which may also change with the temperature. Furthermore, depending on the geometry, it may be more or less difficult to completely remove the oxides between the polysilicon layers during the sacrificial layer etching process.